Metal pigment composition

ABSTRACT

There is provided a process for preparing a low- or non-dusting substantially non-volatile (preferably highly light reflective) metal flake pigment composition, which comprises ball milling atomized metal powder in a milling fluid substantially comprised of water, in the presence of one or more corrosion inhibitors and a substance which acts as a lubricant for the milling process. Optionally, the paste may be formed into granules for easy storage. Preferred metal pigments are aluminum or gold bronze and in one embodiment the metal pigment is aluminum, the lubricant is oleic acid and the corrosion inhibitor is a phosphate ester having a polyethylene oxide side chain. Agent(s) having both lubricating and corrosion inhibiting properties are preferred as additives.

This application is the U.S. national phase application of PCTInternational Application No. PCT/GB97/02912 filed Oct. 22, 1997.

The present invention relates to a process for preparing low- ornon-dusting, substantially non-volatile highly light reflective metalpigment compositions by a ball milling process using water as the majormilling fluid.

The preparation of metal flake pigments is well documented in the patentliterature. For example, U.S. Pat. No. 3901688 describes a wet ballmilling process in which metal powder or chopped foil is milled with anorganic liquid such as mineral spirits and a small amount of a lubricantsuch as stearic or oleic acid. The metal flakes so produced areseparated, for example by wet sieving to provide the desired particlesize distribution and thereafter brought to a paste-like consistency of,typically, 55-80% weight metal content. In this conventional process thelubricant is required to avoid cold welding of the metal flakes underthe action of the grinding media. The purpose of the organic liquid isto reduce the viscosity of the system, enabling efficient conversion ofthe starting powder to flakes.

Metal flakes may also be prepared in the complete absence of solvent bya dry ball milling process, such as that described in U.S. Pat. No.4115107.

A further method of preparation of metal flake is by electrodepositionof a thin film of metal onto an inert support, followed by removal andfragmentation into flakes. The product is generally provided either asdry flake or as a dispersion of the metal flakes in solvent.

The aforementioned methods for preparing metal flake pigments sufferfrom a number of disadvantages. For example, dry milling processes arenow little used, due to the explosive and contaminating properties ofthe dry flake products. Though the paste form, in which the metal flakeparticles are damped by solvent, is inherently safer and easier tohandle, it is not without problems. The 20-45% by weight solvent portionof metal pigment pastes may be acceptable in certain coatingapplications such as automotive paints, but in others, especiallyprinting inks, such solvents typically slow down the drying rate and maycause odour in the final printed film, due to retention of minuteconcentrations of these typically high boiling point solvents. This isespecially disadvantageous in printed films on packaging intended forfood contact. The presence of organic solvent in other applicationareas, such as plastics, can also be very undesirable. The solventvaporises during processing, causing bubbles and surface blemishes inthe pigmented plastic article.

Flake formation by the electrodeposition process can give very brightflakes of narrow particle size distribution, but it is a very costlyprocess, unsuited to large scale production. This is because theequipment required to maintain the hight vacuum environment in which themetal is vaporised is very expensive to construct and operate.

It is also found that the storage stability of the metal pigment pastesthemselves is finite, due to the tendency of the organic solventcomponent to evaporate, leading to aggregation of the metal flakeparticles. This is especially true for pastes in which a more highlyvolatile solvent has been employed, perhaps to ensure the compatibilityof the metal pigment paste in a particular coating system. Onceaggregated, redispersion is difficult. In derived coatings, hidingpower, or opacity, and also gloss, may be greatly reduced.

Increasingly too, environmental concern about organic solvent is leadingto legislation which encourages a lower use of volatile solvents inindustrial processes. The costs associated with solvent purchase,storage and recovery are increasing. Containment equipment, required tomeet increasingly severe legislative constraints on the emission ofsolvent to the atmosphere is expensive. As a result replacement oforganic solvents by water is a strategic goal in many industries.

Recent changes in health and safety classifications require a number ofhigh boiling point petroleum derived hydrocarbon solvents traditionallyused in metal pigment manufacture to be designated carcinogenic. Thisincreases the pressure for their elimination from metal flake pigmentmanufacturing processes.

The need for a stable, safe and easily handled product metal pigmentform, free of the disadvantages of both dry flakes and solventcontaining pastes has been met by the products of European Patent0134676. There is described therein a process for the preparation of asolid low- or non-dusting, metal pigment composition which comprisesforming a coherent paste of an organic binder medium, an organic liquidvehicle and metal pigment, in powder or flake form, the paste beingformed by mixing a first component comprising organic binder medium anda second component comprising metal pigment, with either or both of thefirst and second components comprising organic liquid vehicle and thepaste containing from 3-45% of the organic binder medium based on theweight of the metal pigment, and either sub-dividing the coherentpaste-into particles and removing substantially all organic liquidvehicle from the particles, or removing substantially all the organicliquid vehicle from the coherent paste and sub-diving the resulting massinto particles, at least 98% by weight of the resulting particles beingretained on a sieve having a 150 μm aperture and each containing aplurality of metal pigment particles dispersed in a matrix of organicbinder medium. The so-called “granule” products of this process can beprepared using organic binder media compatible with the end application.Thus, for example, synthetic aldehyde and ketone resins could beemployed for ink applications and polyolefin derivatives for the masspigmentation of thermoplastics.

Though the products of European Patent 0134676 are substantially free oforganic solvent, the process itself still involves processing ofsolvent. It is thus still subject to the aforementioned legislativepressures. There is therefore a clear need for a process for preparingan easily handled, dust free, metal pigment product, which does notemploy organic solvents.

It is possible to prepare a dust free, metal pigment product without theuse of organic solvents if the metal pigment is prepared by dry millingand thereafter incorporated into a suitable organic carrier material bymixing at a temperature above the melting point of the organic carrier.Once a homogeneous mixture has been attained, the mass is cooled, oftenwith extrusion into a more easily handled form, such as granules orpellets. Such processes were once widely employed for the preparation ofplastics masterbatch. The need to use dry metal pigments, with theirattendant disadvantages, and the difficulty of wetting such pigmentssatisfactorily into the carrier resin, have contributed to the declinein this type of process. Although the problem of metal flake dusting maybe reduced if the metal powder precursor is milled in the presence ofthe carrier resin, methods traditionally used to separate wanted fromunwanted particle size fraction, such as dilution with solvent andscreening, are then no longer operable.

A more satisfactory processing liquid is water. It is readily available,inexpensive and nonflammable. However, a difficulty arises in the caseof the more reactive metal pigments, especially aluminum, which is themost widely used of such pigments. Aluminum metal may react with waterto form aluminum oxide and hydrogen gas, according to the equation:

2Al+6H₂O−>2Al(OH)₃+3H₂

Generation of hydrogen is dangerous, because it is highly explosive.Sealed containers of aqueous metal pigment pastes may become pressurisedand explode. In addition, the pigmentary properties of the metal flakeare destroyed.

Many attempts have been made to stabilise aluminum against thisreaction. Methods employed fall into several categories, for exampleresin encapsulation or chemical treatment. As an example of the former,there may be mentioned U.S. Pat. No. 4213886. Prominent types ofchemical treatment are silica coating (see, for example, U.S. Pat. No.2885366), treatment with chromium derivatives (German Patent 3636183),phosphate treatment, described in European Patent 0319971 and vanadiumtreatment (European Patent 0104075).

Milling aluminum powder in a mixture of water and an organic solvent hasbeen described in U.S. Pat. No. 3565655. Morpholine is used as acorrosion inhibitor with a fatty acid as the milling lubricant. However,the presence of at least 2 weight percent of a hydrocarbon or ahalogenated hydrocarbon is a necessary part of the invention.

U.S. Pat. No. 4693754 describes the milling of aluminum powder in amixture of hydrocarbons, water, and a compound of chromium or vanadiumwhich acts as a corrosion inhibitor. However again the presence of someorganic solvent in the milling process is a component part of-theinvention.

In WO-A-94/28074 there is described for the avoidance of odour themilling of aluminum powder, optionally with solvent or water, without afatty acid lubricant, but in the presence of a polymer resin that is apaint or ink binder. This Patent Application does not include the use ofa corrosion inhibitor in the milling process. In the absence of acorrosion inhibitor, water milled aluminum pigments are prone to severegassing and result in products having a dull grey colour, in contrast tothe bright metallic effects desired for decorative metallic finishes.

There is, therefore, still a need for a satisfactory process which canbe used for milling aluminum powder and the like without organicsolvent.

According to the present invention, there is provided a process forpreparing a low- or non-dusting, substantially non-volatile (preferablyhighly light reflective) metal flake pigment composition, whichcomprises ball milling atomised metal powder in a milling fluidsubstantially comprised of water, in the presence of one or morecorrosion inhibitors and a substance which acts as a lubricant for themilling process.

Thereafter, unwanted oversize or undersize particles may be removed. Inthe next stage of the process the aqueous metal pigment slurry may beused unaltered, may be converted to a dry metal flake pigment powder byremoval of the milling fluid, for example at elevated temperature, or ispreferably concentrated to a pastelike consistency. The metal flakepigment can be incorporated in an organic binder medium by mixing toform a coherent paste of an organic binder medium, water and metal flakepigment, the paste being formed by mixing a first component comprisingorganic binder medium and a second component comprising metal pigment,with either or both of the first and second components comprising waterand the paste containing from 1 to 150%, preferably 3-70%, and mostpreferably 30 to 60% of the organic binder medium based on the weight ofthe metal pigment, and either sub-dividing the coherent paste intoparticles and removing substantially all volatile liquids from theparticles, or removing substantially all the volatile liquids from thecoherent paste and sub-dividing the resulting mass into particles, atleast 98% by weight of the resulting particles being retained on a sievehaving 150 μm aperture and each containing a plurality of metal pigmentparticles dispersed in a matrix of organic binder medium, the organicbinder medium being capable of binding the metal flake pigment particlesby either precipitation from solution during volatile liquid removal, ormelting or sintering at elevated temperature and fusion.

The volatile liquid will usually consist substantially of water. Forexample, the volatile liquid may be water together with small amounts ofadditives, for example lower alcohols as wetting agents and resinsolubilisers and dispersers.

The milling fluid used in the present invention consists substantiallyof water. The presence of up to 50% by volume (for example up to 30%,especially up to 25%⁻, more especially up to 10%) of an organic solventcan usually be tolerated. A small amount (for example less than 2%) ofan organic solvent is generally acceptable. Lower alcohols areespecially useful as defoaming agents. Any such organic solvent isdesirably water miscible. In one embodiment the milling fluid consistsonly of water and the system contains no organic liquid at all, the onlyorganic compounds present being additives such as the lubricant(s),corrosion inhibitor(s) etc.

One of the advantages of the process of the present invention is thepossibility of treating the milled flakes whilst in an aqueous system.For example, the milled flakes can be chromate treated or coated withsilica or alumina prior to any granule formation. Such a process enablesthe pigments to be rendered suitable for different applications or tohave different colour characteristics. Such aqueous treatments are knownin the art, but tend to be difficult and expensive to carry out sincethe traditional milling fluid must be removed before the pigments can betreated in an aqueous medium. Since the milling process of the presentinvention is carried out in water, such treatments are simple toconduct.

The substantially aqueously carried product of the milling step could beadded to surface coating binders dissolved or dispersed in water,solvent or mixtures of the two, to prepare a surface coating, such as anink or paint. The reaction of certain metal flake pigments, notablyaluminum, is, however unpredictable. As such a surface coating containsa proportion of water there exists the possibility that reactions mayoccur during storage, with the formation of hydrogen gas and associatedhazards.

It is a further advantage of the process of the invention that water issubstantially eliminated from contact and potential reaction with themetal pigment through the formation of the substantially non-volatilemetal pigment composition.

Metals suitable for the performance of the invention include all thosemetals commercially employed as flake pigments, such as aluminum, zinc,copper, tin, nickel, iron and alloys thereof, such as gold bronze (analloy of copper and zinc) or stainless steel (an alloy composed mainlyof iron, nickel and chromium). Aluminum and gold bronze are preferred.There is no criticality to the particle size of the milled flakes, but aflake diameter range of 6 μm to 600 μm, preferably 10 μm to 300 μm isgenerally suitable. Advantageously, the particles produced are wellflattened highly light reflective flake pigments.

Any compounds capable of inhibiting the reaction of the metal with watermay be employed as corrosion inhibitors, for example phosphorus-,chromium-, vanadium- or silicon-containing compounds. They may be usedindividually or in admixture.

Suitable phosphorus compounds may be organic or inorganic. Simpleinorganic phosphates, such as calcium or magnesium phosphate, or morecomplex phosphosilicate compounds may be used. The latter includecalcium phosphosilicate, calcium strontium phosphosilicate and aluminumzirconium zinc phosphosilicate. An especially preferred member of thisclass is calcium strontium zinc phosphosilicate. organic phosphoruscompounds include alkyl and dialkyl phosphates and phosphites, with thealkyl groups containing 2-20 carbon atoms. Iso-octyl acid phosphate maybe particularly mentioned. Also suitable are phosphate esters of longchain ethoxylated alcohols. Preferred amongst these is Briphos S2D, aproduct of the Albright & Wilson company, which is an ethoxylatedphosphate ester.

Silicon containing compounds capable of inhibiting the reaction ofmetals with water include organic silanes and silicates, especiallytetraethyl silicate, and inorganic silicon compounds such as potassiumsilicate.

Salts of molybdenum, vanadium and tungsten, especially the ammoniumsalts, have also shown particular suitability in the process of theinvention.

Chromium compounds suitable for the process of the invention includeammonium dichromate and chromic acid. In this class, the former ispreferred as it is less aggressive towards metal grinding media.

Amongst the above corrosion inhibiting compounds, non-resinous organicor inorganic phosphates are especially preferred. They generally offer ahigh level of metal passivation with few health and safety concerns.

Lubricants suitable for the process of the invention are generallyorganic compounds recognised in the art as having surfactant properties.Non-ionic surfactants, such as ethylene oxide condensates with aliphaticalcohols or phenols are effective without affecting the pH of thesystem. In general it is desirable that the pH is kept as close toneutral as possible to assist in the prevention of corrosive attack ofthe metal surface. Such lubricants may also be advantageous in the metalsegregation and recovery stages of the process, for example to overcomethe surface tension of water to ensure efficient screening.Surprisingly, fatty acids, such as oleic and stearic acids, widely usedas lubricants in the solvent based ball milling of metal powders, arealso effective in the milling step, especially when made active in theaqueous phase by surfactants or by formation of a water soluble alkalisalt. In the same way, water insoluble plasticisers may be used, forexample phthalates such as dioctyl or diisodecyl phthalate, andadipates, such as dioctyl adipate.

Also suitable as lubricants are polyethylene oxides and glycols andpolypropylene oxides and glycols of various molecular weights. Thosedisplaying some water solubility are preferred.

It may also be desirable to add small quantities of organic compoundsrecognised in the art for their defoaming properties. For example,acetylenic diols may be used, but the inexpensive lower alcohols arealso effective.

Advantageously, surfactants may be employed. Examples include anionic,non-ionic and cationic surfactants, including the solid alkyl etherphosphates such as the “Crodafos CS” (Registered Trade Mark) range ofCroda Chemicals Ltd, alkylaryl sulphonates and their alkali metalderivatives such as alkali toluene sulphonates, alkali xylenesulphonates, alkali naphthalene sulphonates, alkali diisopropylnaphthalene sulphonates and alkali dodecyl benzene sulphonates; alcoholsulphates such has sodium lauryl alcohol sulphate, sulphosuccinates suchas sodium dioctyl sulphosuccinate, sarcosinates such as lauroylsarcosine and stearyl sarcosine; fatty amines such as stearylamine, anddistearylamine; amine salts such as coconut fatty amine acetate; alkylphenol ethoxylates such as nonyl phenol ethoxylate; alcohol ethoxylatessuch as higher ethoxylated oleyl alcohol; higherpolyoxypropylene-polyoxy ethylene copolymers, such as alkylolamides suchas myristic diethanolamide and coconut mono-isopropanolamide, esterssuch as propylene glycol monostearate and cetyl palmitate; maleicanhydride copolymers such as the disodium salt of maleic anhydride anddi-isobutylene, and the SMA series of low molecular weightstyrene-maleic anhydride copolymers.

Phosphate esters (eg Biophos S2D) which also have lubricating and/orcorrosion inhibiting properties are preferred.

In a preferred embodiment, additive(s) having corrosion inhibiting,surface tension reducing and lubricating properties are present in themilling step.

Milling lubricants prevent cold welding of flakes which typically takesplace during the ball milling process. The corrosion inhibitor andmilling lubricant functions may be provided by a single chemicalsubstance, for example a substituted phosphate ester (such as BriphosS2D), or the functions may be provided by two or more differentmaterials.

There is no criticality to the mechanism of comminution. Any comminutionprocess known in the art for metal flake production may be employed,providing the mechanical energy imparted is not so severe as to damagethe metal flakes being formed. Ball milling is a widely operatedprocess.

Neither is there any criticality to the grinding media, providing theydo not react chemically with the other components during or after thecomminution stage of the process. Stainless steel and high densityceramic grinding media are generally satisfactory.

Unwanted oversize or undersize metal flake particles are removed by anysuitable means, such as screening of a slurry diluted by more water. Theaqueous metal pigment slurry can then be concentrated to a paste by anconvenient means, such as a filter press, ready for admixture with theorganic binder medium.

Organic binder media include those organic materials habitually employedas binders in paints and inks or as plastics masterbatch carriers. Theorganic binder chosen is dependent on the envisaged end use of theproduct of the invention. Thus, if desired, the binder can be asolvent-soluble resin. As examples of organic binder media there may bementioned cellulose acetate butyrate (CAB) and cellulose acetatepropionate (CAP) resins, coumarone indene, epoxy esters, epoxidemelamine and epoxide phenolic condensates, ketone, aldehyde, maleic andphenolic resins and also rosin, cellulose and petroleum derived resins,together with thermoplastic polymers, such as polyacrylates,polyolefins, polyvinyls, styrenics, polyamides, polyesters andcopolymers thereof. Also suitable are natural and synthetic waxes, suchas montan and paraffin wax and synthetic waxes such as polyethylene andpolypropylene waxes. Where it is desired to introduce liquid organicbinders, such as plasticisers, for example-to improve applicationproperties, they are desirably added in minor proportions in combinationwith solid resins, to provide structural rigidity in the resulting metalpigment particles. Such plasticisers include mineral oils as well asphthalates such as dioctyl or diisodecyl phthalate, and adipates such asdioctyl adipate.

Gelatin and carrageenen are useful water soluble organic binders due totheir suitability for food contact applications.

In a preferred embodiment the binder material is a non-resinousmaterial.

The products of the invention are typically in a form, such as tablet,pellet, granule, flake or spherical bead, which provides the attributesof ease of handling, low- or non-dusting and meterability. Granuleshaving a length of 5-20 mm, a cylindrical cross section and a diameterof 1.5-3 mm are preferred, as they have been found to offer optimumhandling characteristics, especially in plastics applications where itis important to prevent stratification of polymer pellets and theparticularly dense products of the invention. Apparatus used for thepreparation of such physical forms is well known to those skilled in theart and is described in, for example, European Patent 0134676.

The function of the organic binder medium is to bind the metal pigmentflakes together to prevent them becoming airborne as dust. Where theorganic binder medium is soluble or dispersible in water, it may beadded as an aqueous solution or dispersion. Where it is insoluble inwater it is preferable to micronise the binder. In this latter case, thecoherent paste of metal pigment, water and micronised organic bindermedium is formed into particles, for example by mixing and extrusion,then dried at for example 60° C. to remove substantially all the water,then heat treated at elevated temperature, for example 100 to 130° C.for a short time, to fuse together the micronised organic binder mediumand the metal pigment. This process is particularly suited to productsfor the plastics market, in which suitable organic binder media tend tobe insoluble in water. It provides a final product form which hasexcellent colouristic and application properties when used in theinjection moulding or extrusion of thermoplastics.

In extreme cases the chosen binder may be insoluble in water andunsuitable for micronising and fusion. In such cases the binder may bedissolved or dispersed in a suitable organic solvent prior to admixturewith the metal pigment component. Such a solvent is desirably, thoughnot essentially, water miscible.

In a preferred embodiment the metal is aluminum. Conveniently thelubricant is a mixture of a surfactant and a fatty acid, such as oleicor stearic acid. Oleic acid in an amount of 1 to 100%, preferably 2 to60%, most preferably 3 to 8%, for example approximately 5%, by weightrelative to the metal has been found to be effective in mixture withnon-ionic surfactants at 5-1.5%. The corrosion inhibitor mayadvantageously be a phosphate ester having a polyethylene oxide sidechain.

The invention is further illustrated by the following Examples in whichall parts and percentages are by weight, unless otherwise stated.

EXAMPLE 1

To a cylindrical mill of diameter 21 cm were added:

5000 g of ⅛ inch (3.2 mm) diameter stainless steel balls;

500 g of distilled water;

100 g of fine particle size, aluminum powder; and

13 g of Briphos S2D, which had been pre-neutralised withtriethanolamine—this makes the Briphos more soluble and reduces attackof the aluminum. Briphos S2D is a phosphated ester of a long chainethoxylated alcohol manufactured by Albright and Wilson. The mill wasrotated at 80 rpm for 4 hours and the aluminum pigment so formedseparated from the steel balls by sieving, prior to recovery in a filterfunnel.

In a laboratory mixer, a quantity of the aluminum flake pigment thusobtained, containing 25.0 g solids, was added to 10.7 g Hoechst Ceridust3620, a micronised polyolefin wax with a particle size of less than 22microns. The mixture was formed into granules by extrusion through a 2mm diameter die, and dried in an oven held at a temperature of 60° C.⁻+/−10° C. for two hours. The granules were then placed in an oven heldat 115° C.+/−10° C. for 10 minutes to fuse the organic binder medium.35.1 g of substantially water free, nondusting, free flowing, meterablegranules of approx. 12 mm length and of good abrasion resistance wereobtained.

A test piece made by injection moulding the granule in polystyrene at alevel of 1% calculated on polymer weight, had a smooth, fine and brightsilvery appearance.

EXAMPLE 2

The following mixture was milled in a cylindrical mill as described inExample 1, with the following formulation:

5000 g of ⅛ inch (3.2 mm) diameter stainless steel balls;

500 g of distilled water;

100 g of aluminum powder of approx. 33 μm average particle diameter;

13 g of Briphos S2D, which had been neutralized with triethanolamine;

2.85 g of Antarox V27, a linear C₈₋₁₀ aliphatic alcohol;ethoxylate/propoxylate alcohol manufactured by Phone-Poulenc Chemicals;and

0.15 g of Surfynol 104, an acetylinic diol from Air Products.

A quantity of the derived aluminum flake pigment paste, containing 24.1g solids, was added to 10.3 g of FE 532-00, a micronised ethylene vinylacetate resin sold by Croxton and Garry. The mixture was granulated,dried and heat treated as in Example 1. A test piece made by injectionmoulding the granule in polypropylene at a level of 3%, calculated onpolymer weight, had a bright, highly sparkling, silvery appearance.

EXAMPLE 3

The method of Example 1 was repeated with the substitution of HoechstCeridust 3620 by an equal weight of Polyox WSR 301, a solid, non-ionic,high molecular weight, water-soluble, polyethylene oxide polymer. Themixture was formed into granules by extrusion through a 2 mm diameterdie, and dried in an oven held at a temperature of 50° C.+/−10° C. forfour hours. 35.2 g of substantially water free, non-dusting, freeflowing, meterable granules of approx. 12 mm length and of good abrasionresistance were obtained.

An aqueous printing ink was prepared by combining the following:

20 g of the granule product of this Example, dispersed in 25 g water andlet down with

53 g Zinpol 132, an acrylic resin emulsion of 40% solids, supplied byWorlee Chemie and

2 g waxes and defoaming additives.

The ink thus formed was stable to gassing and provided a smooth, brightmetallic silver effect when printed on a paper substrate.

EXAMPLE 4

10 g Halox ZSP 391, a calcium strontium zinc phospho-silicate compound,sold by Halox Pigments of Hammond, Ind., United States of America.

3 g oleic acid,

5 g Pluriol 600, a polypropylene glycol supplied by BASF A.G., and

50 g deionised water were high speed stirred to solution.

35.1 g of solution,

219.4 g deionised water, and

30 g atomised aluminum powder of approx. 8 μm average particle diameter

were set on a vibratory mill with 1500 g ⅛ inch (3.2 mm) diameterstainless steel balls, in a rigid plastic pot. After 4 hours, thecontents were removed and separated from the steel balls. Water wasadded to a metal concentration of about 3% and the slurry screened on a400 mesh screen. The undersize fraction was concentrated in a filterpress to about 80% metal content, then combined with Microthene 532-00,an ethylene vinyl acetate polymer sold by Croxton & Garry Ltd, by thefusion process of Example 1.

When injection moulded at 1.5% w/w in polypropylene, the granuleexhibited a particularly bright, reflective silver coloration, with gooddispersion.

The dispersibility characteristics of this product can be furtherenhanced by replacing up to 30% of the Microthene by a high boilingmineral oil such as Kaydol, manufactured by Witco.

EXAMPLE 5

200 g Halox SZP-391

100 g Pluriol P600

100 g Antarox V27

100 g water and

60 g oleic acid

were high speed stirred for 10 minutes to form a homogeneous mixture. Toa cylindrical mill of diameter 21 cm were added: 5000 g of ⅛ inch (3.2mm) diameter stainless steel balls, 75 g of the above mixture, 100 galuminum powder of 91 m median particle diameter and 375 g of distilledwater.

The mill was rotated at 105 rpm for 6 hrs to form a flake pigmentproduct of approximately 25 μm median particle diameter. The grindingmedia were removed on a coarse screen and the product itself screened ona 400 mesh (38 μm) screen using water as the washing liquid. The flakepassing through the screen was concentrated on a filter funnel. When.converted to a granule and tested in the water based ink system ofExample 3, this material provided a bright silver effect with goodcoverage and good adhesion to a paper substrate.

The Halox SZP-391 of this Example may be replaced by members of theHeucophos range of multiple metal phosphates manufactured by HeubachGmbH, with similar results.

EXAMPLE 6

19 g Antaroz V27 and

1 g Surfynol 104

were warmed and mixed together to form a homogeneous liquid, which wasmixed into 120 g of the water based paste intermediate of Example 1,containing 80 g metal, to form a stiff paste. The paste was extrudedthrough a 2.5 mm diameter die into strands and the water removed bydrying at 70° C. The resulting dry strands were broken up into granulesof approximately 1 cm length. An aqueous ink was prepared bypredispersing the granules in a small quantity of water into which theZinpol medium of Example 3 ws thereafter blended. A bright ink, withgood stability and coverage was obtained.

The Antarox and Surfynol in this example may be replaced by 20 g of thenatural product carrageenen in powder form with similar results. Such agranule has particularly good shelf life and redispersion in water.

EXAMPLE 7

To a 0.5 litre capacity vibratory pot mill were added:

1.5 kg of 2.4 mm diameter ceramic grinding media,

150 g water,

30 g aluminum powder of 7 μm average particle diameter,

2.5 g iso-octyl acid phosphate and sufficient 25% aqueous ammonia tomaintain the pH at approximately 7.

The charge was milled for 3 hrs then recovered, screened, formed intogranules and tested as in Example 5. The printed ink had similarbrightness, but superior coverage to that of Example 5.

EXAMPLE 8

To 0.5 litre capacity vibratory pot mill were added:

1.5 kg of 3 mm diameter stainless steel grinding media,

150 g water,

30 g aluminum powder of 7 μm average particle diameter,

2.4 g Briphos S2D and

0.6 g 25% aqueous ammonia.

The charge was milled for 4 hrs, then discharged with water and screenedon a 400 mesh (38 μm) screen. The fraction passing through the screenwas collected and concentrated under vacuum in a filter funnel. Aquantity of the filter cake, corresponding to 80 g metal was thoroughlymixed with 20 g of a commercial source of C₂₋₁₄-aliphatic alcohols. Thestiff paste was formed into pellets and the water removed at 65° C. Theresulting product had good stability and colouristic properties in a onepack UV curing resin system.

EXAMPLE 9

The milled, screened and recovered paste product of Example 8 was mixedwith micronised Laropal K80 ketone resin, manufactured by BASF AG in theratio 80 parts by weight of metal to 20 parts by weight of resin. Themixture was formed into granules by extrusion and the water removed inan oven of 70° C.

When tested in a solvent based ink, the granular product displayedsimilar characteristics to a granule prepared by the methods describedin EP-A-0134676 using a conventional solvent milled paste as startingmaterial.

EXAMPLE 10

An amount of the milled, screen and recovered paste product of Example 8corresponding to 80 g metal was placed in a 1 litre beaker fitted with apropeller agitator set at 400 rpm. With agitation there were then added,

530 g Dowanol PB29, an ether-alcohol solvent of the Dow Chemical Co,

26.7 g of 25% aqueous ammonia,

20 g tetraethyl silicate and finally another

26.7 g of 25% aqueous ammonia.

The mixture was agitated for 5 minutes, then there was added another26.7 g of 25% aqueous ammonia.

After a further two hours mixing, air was bubbled through the slurry for2 hours to remove excess ammonia and the metal recovered on a Buchnerfilter. Thereafter, the filter cake was converted to a gold pigment bythe process of Example 1 of our co-pending British Patent Application No9609507.0 (ie was stirred at 600 rpm with a paddle agitator for onehour, then filtered under vacuum on a Buchner funnel, and washed withexcess water. The product was a viscous paste dispersible in both waterand oxygen-containing hydrocarbon solvents) and then to a granule by theprocess of Example 25 of EP-A-0134676. The granules so formed provided arich gold coloration in water based paints and inks.

EXAMPLE 11

2 g of oleic and

2 g of Antarox V27 and Surfynol 104 in 19:1 weight ratio were mixedtogether and added dropwise to

140 g vigorously stirred water in a beaker containing 1 g⁻isopropanol,to form an emulsion. There was then added

4 g hydrogen peroxide (30%w/w; 100 volume) and the whole added to

30 g A 7401 atomised aluminum powder of 8 μm average particle diameterin a ball milling pot of 500 ml volume containing

1500 g spherical, stainless steel grinding media of 3 mm averagediameter.

The pot was sealed and placed on a vibratory mill for 4 hours. Thecharge was washed out with 200 g water, screened on a 400 mesh screenand an aqueous paste recovered by vacuum filtration. The water wasremoved by drying at 50° C. and 16 g of the resulting fine flake powderincorporated into 8.89 g Worleesol 31, a modified linseed oil polymer(supplied by Worlee Chemie as a 45% solution in 80/20 w/w water/2-butoxyethanol), further diluted in 3.5 g of a 60/40 weight ratio mixture ofwater and isopropanol.

After forming into granules and evaporating the volatiles at 60° C., thesoft, dry product was found to give a bright, high coverage silverfinish in an exclusively isopropanol based or water/isopropanol basedvarnish.

EXAMPLE 12

A formulation comprising

1500 spherical, ceramic grinding media of 3 mm average diameter,

150 g water,

30 g aluminum powder of 8 μm average particle diameter,

2.4 g Crodafos 25D5A, an ethoxy (5) C₁₂₋₁₅ alcohol acid phosphate ester,supplied by Croda Ltd and

0.6 g ammonia, 25% in water was loaded into a 500 ml pot and milled on avibratory mill for 3 hours.

The grinding media was removed on a coarse screen and the metal flakepigment product screened on a 400 mesh (38 μm) screen using water as thewashing liquid. The flake passing through the screen was concentrated ona filter funnel. When converted to a granule with a carrageenan carrierand tested in the water based ink system of Example 3, this materialprovided a bright silver effect with good coverage.

EXAMPLE 13

The method of Example 12 was repeated with the substitution of Crodafos25D5A by an equal weight of Crodafos T5A, an ethoxy (5) isotridecanolacid phosphate ester. Similar results were obtained on conversion to agranule and testing as described therein.

EXAMPLE 14

The method of Example 12 was repeated with the substitution of Crodafos25D5A by an equal weight of Crodafos N10N, an ethoxy (10) oleyl alcoholphosphate ester diethylamine salt. Similar colouristic results wereobtained on conversion to a granule and testing as described therein.This material, however, also had outstanding adhesion to the papersubstrate, as demonstrated by a tape test.

EXAMPLE 15

A formulation comprising

1500 spherical, stainless steel grinding media of 3 mm average diameter,

150 g distilled water,

30 g aluminum powder of 254 m average particle diameter and

2 g octyl phosphonic acid was charged to a 500 ml pot and milled on avibratory mill for 1.5 hours.

After removing the grinding media, the milled material was screened on a325 mesh (45 μm) screen and recovered as a granule by the method ofExample 12 using as carrier a water soluble part hydrolysed polyvinylacetate resin. The 80% metal content granule provided a very bright,sparking coating based on Joncryl 537, an aqueous acrylic industrialpaint resin manufactured by S C Johnson.

EXAMPLE 16

Aluminum pigment, made by the process of example 1 as ha water carriedpaste containing 40 g of aluminum metal, was mixed with 13.3 g of BeetleBE 370, hexamethoxymethyl melamine from BIP Speciality Resins Ltd. Themixture was formed into granules by extrusion through a 2 mm diameterdie, and dried in an oven held at a temperature of 60° C. for 16 hours.

An aqueous printing ink was made by dispersing 5 g of the dried granulein 5 g of distilled water, and then mixing this dispersion with 15 g ofGlascol LS2, a colourless water-based ink from Allied Colloids. Adrawdown on to white paper showed that the product had a bright metallicsilver colour.

EXAMPLE 17

The procedure of example 16 was repeated with the Beetle BE 370 replacedby RC-294-J427, an acetylenic diol surfactant from Air Products andChemicals Inc. The dried granular product so formed gave a brilliantmetallic silver effect when made up into a Glascol LS2 ink.

EXAMPLE 18

A dispersion of

7.5 g Molywhite 212, a basic calcium zinc molybdate from SherwinWilliams Chemicals

1.5 g oleic acid

2.5 g Pluriol P600

2.5 g Antarox V27

25.0 g distilled water was added to

30 g of a fine particle size aluminum powder

100 g distilled water

1500 g of ⅛ inch diameter stainless steel balls and milled on avibratory mill for 3.5 hours.

A flaked aluminum paste product was extracted from the grinding media.If required, the paste can be converted into granular form as describedin previous Examples.

What is claimed is:
 1. A process for preparing a low- or non-dusting,substantially non-volatile metal flake pigment composition, said processcomprising ball milling atomised metal powder in the presence of amilling fluid, together with one or more additive(s) which togetherexhibit lubricating, corrosion inhibiting and surfactant properties,wherein the lubricant is not suet; wherein said milling fluid consistsof water with a maximum content of organic solvent of 10% by weight. 2.A process as claimed in claim 1 which includes the step of screening themilled composition to select particles of a pre-selected size.
 3. Aprocess as claimed in claim 1 and which includes the step of forming acoherent paste of an organic binder medium, water and metal flakepigment.
 4. A process for preparing a low-or nondusting, substantiallynon-volatile metal flake pigment composition, said process comprising:(a) ball milling atomised metal powder in the presence of a millingfluid, together with either an additive having both lubricating andcorrosion inhibiting properties or with a lubricant and at least onecorrosion inhibitor, wherein said milling fluid consists of water with amaximum content of organic solvent of 10% by weight, to produce a metalflake pigment; and (b) forming a coherent paste of an organic bindermedium, water and said metal flake pigment, wherein said paste is formedby mixing a first component comprising organic binder medium and asecond component comprising said metal flake pigment, with either orboth of the first and second components comprising water and the pastecontaining from 3-70% of the organic binder medium based on the weightof the metal flake pigment, and either sub-dividing the coherent pasteinto particles and removing substantially all volatile liquids from theparticles, or removing substantially all volatile liquids from thecoherent paste and sub-dividing the resulting mass into particles, atleast 98% by weight of the resulting particles being retained on a sievehaving 150 μm aperture and each containing a plurality of metal pigmentparticles dispersed in a matrix of organic binder medium, wherein theorganic binder medium binds the metal flake pigment particles by eitherprecipitation from solution during volatile liquid removal, or sinteringor melting at elevated temperature and fusion.
 5. A process as claimedin claim 4 wherein said lubricant comprises an ethylene oxide condensatewith alcohols or phenols, and a fatty acid or a derivative thereof.
 6. Aprocess as claimed in claim 4 wherein said corrosion inhibitor is aphosphorus-, chromium-, vanadium- or silicon-containing compound.
 7. Aprocess as claimed in claim 6 wherein said corrosion inhibitor is aphosphate ester having a polyethylene oxide side chain.
 8. A process asclaimed in claim 4 wherein a single moiety acts as lubricant andcorrosion inhibitor.
 9. A process as claimed in claim 8 wherein saidmoiety is a phosphate ester having a polyethylene oxide side chain. 10.A process as claimed in claim 4 wherein a surfactant is present in saidmilling step.
 11. A process as claimed in claim 4 wherein the metalpigment is an aluminum, zinc, copper, tin, nickel or iron pigment or apigment of an alloy comprising aluminum, zinc, copper, tin, nickel, oriron.
 12. A process as claimed in claim 4 wherein the metal pigment isan aluminum or gold bronze pigment.
 13. A process as claimed in claim 4wherein the metal pigment is a light reflective pigment.
 14. A processas claimed in claim 4 wherein the metal pigment is aluminum, thelubricant is oleic acid and the corrosion inhibitor is a phosphate esterhaving a polyethylene oxide side chain.
 15. A process as claimed inclaim 4 which includes a step of treating the metal pigment flakeswhilst in an aqueous system following the melting step and prior toforming the metal pigment particles.
 16. A process as claimed in claim15 wherein said milled metal pigment flakes are treated with chromate,coated with silica or coated with alumina.
 17. A process as claimed inclaim 4 wherein said pigments are coated with micronised binder beforeparticle formation and then sintered to produce said metal pigmentparticles.
 18. An organic solvent-free paste comprising a ball-milledmetal flake pigment, water and agent(s) having lubricating and corrosioninhibiting properties, wherein said metal flake pigment is produced byball-milling metal powder in a water-based milling fluid.
 19. A paste asclaimed in claim 18 comprising ball-milled aluminum or gold bronze flakepigment, water and a phosphate ester having a polyethylene oxide sidechain.
 20. A metal pigment composition in granular form containing aplurality of milled metal flake pigments dispersed in a matrix oforganic binder medium without any organic solvent present wherein saidmilled metal flake pigments are provided by milling using a water-basedmilling fluid.
 21. A metal pigment composition in granular form asclaimed in claim 20 which is produced by sintering and wherein saidmetal flake pigments are dispersed in a matrix of micronised organicbinder medium.